1. Field of the Invention
The present invention relates to prosthetics and, more particularly, to a prosthetic socket centering block to allow convenient mounting of prosthetic limbs for above-the-knee and below-the-knee amputation patients at selectable flexion angle and offset.
2. Description of the Background
There are a variety of different types of prosthetic devices for patients that have had either transfemoral (above-knee) or transtibial (below the knee) amputation. Typically, post-operative prosthetic devices for either type of amputation begins with a liner that is rolled onto the residual limb. The liner is a soft, stretchy material that acts as an interface with the prosthesis.
Once the liner is on, the residual limb then slides into a hard socket. This socket is specially made to fit and can be made out of a variety of materials.
The hard socket for a transfemoral prosthesis has a knee joint connected to it, and the more fluid and natural the movement of the knee the better. Transtibial prosthetics have no knee joint. In both cases (with or without a knee joint) there is typically an aluminum or carbon fiber tube to which a foot module is connected.
For example, U.S. Pat. No. 5,653,766 to Naser issued Aug. 5, 1997 shows a prosthetic device 20 having a generally cylindrical socket 24 with an opening for receiving an amputated limb. The socket 24 is closed at the other end, and is mounted on a bendable knee joint. Once the limb is properly received within the socket 24, straps 38 are adjusted so that a secure fit is achieved. The patient then is able to walk using the prosthetic device 20.
With all such transfemoral and/or transtibial prosthetics (above & below the knee), it is very important that the socket be securely fitted to the limb and secured in place. Stability is a common problem as many existing anchoring systems use a single attachment point to hold the residual limb in place, and this typically leads to extraneous pivoting, rotation and shift during ambulation. The prior art ICEX® Socket System uses a combination lanyard and pin kit as a docking and locking mechanism. The socket has a distal pin that docks with the prosthesis. A lanyard is connected to the liner through a slot in the bottom of the socket. The lanyard is pulled to allow the patient's residual limb, which is enclosed in the silicone liner, to be drawn into the socket by the lanyard. The lanyard is then anchored to the front of the socket.
There are also a number of “suspension” type sockets that eliminate the pin. U.S. Pat. No. 6,645,253 to Caspers issued Nov. 11, 2003 shows a suction system that employs a vacuum pump to impart suction to the liner, the vacuum pump doubling as a shock absorber for the artificial limb. Commercially, this is known as the Harmony® System which pulls air from the sealed socket and evacuates moisture (sweat) buildup. A nonporous polyurethane liner (not shown) is fitted over the residual limb and is inserted in the socket. A vacuum pump is attached via a connector block beneath the socket to create a vacuum force which is coupled by a tube to the liner, thereby evacuating air and sealing it to the residual limb. This provides a total-contact hypobaric suction equal weight distribution socket liner which tacks up to the skin of the residual limb and provides total contact with the limb.
U.S. Pat. No. 6,793,682 to the present inventor discloses a “Sure-fit Prosthetic Attachment System” (known commercially as the KISS® System) for transfemoral and/or transtibial prostheses, comprising a liner for enveloping an amputee limb. The liner has a strap attached at one end to a reinforcement plate that is sewn and/or bonded to the liner toward the top, and a buckle is attached to the other end of the strap and is suspended thereby from the liner. Another strap is fixedly attached to the bottom end of the liner. The anchoring system also includes a containment socket for seating the liner. The containment socket has a pair of slots there through at positions corresponding to the buckle and strap of the liner, respectively. To apply the anchoring system, the patient first applies the liner to his/her limb. The liner is then inserted into the socket with the fastening strap and buckle protruding out through the respective slots. The fastening strap is then threaded up through the buckle (running upward along the side of the socket) and is inserted there through. The patient pulls down on the strap, which works by pulley action to draw the liner down into the socket until the liner is securely seated in the socket. When fully seated, the fastening strap is secured to itself by Velcro®. The foregoing forms a suspension which holds the prosthesis on. Moreover, the fastening straps through slots absolutely prevent lateral shift as well as rotation. On the other hand, the patient need only readjust the Velcro® closure to adjust the position of the limb within the socket. Thus, if the limb changes position because of volume change and the distal migration of the limb into the socket, the prosthesis can easily be adjusted to compensate.
One of the primary concerns of prosthesis design and construction is that the device be lightweight and provide a comfortable fit to the residual limb, and it is extremely important to emulate a natural gait when in use. To provide the user with a comfortable and natural gait, it is of primary concern that the prosthesis be properly aligned so that its movement conforms to the shape and movement mechanics of the wearer's body. The goal is to duplicate the normal knee position and alignment. Taking the time to properly bench align a prosthesis contributes to a smooth, energy efficient gait pattern. A proper bench alignment controls knee flexion after heel strike, ensures smooth rollover with limited hyperextension, and controls “heel off” prior to initial contact on the other foot. Generally, a small degree of socket flexion (anterior tilt in the socket with respect to the foot) is desirable to assist better loading in the socket and help create a smoother gait pattern. Flexion in the socket positions the limb in a natural midstance position and helps reduce hyperextension tendencies during gait. As seen in FIG. 1, normal socket flexion should be set to a 5-7 degree angle, though it may vary in different situations when contractures are present (muscle contractures result from muscle imbalance problems associated with the prosthetic). In addition to socket flexion angle, the center of the foot should be offset from the knee joint. For this, the center of the foot is normally placed 30 mm in front of the alignment reference line and mounted with plantar flexion. Presently, more than normal (greater than 7 degree) offset and flexion angle are achieved with external-to-the-socket offset angled flexion plates, as seen in FIGS. 2 and 3, which are typically provided in a range of flexion angles (each fixed at a particular angle). The prosthetic pylon and knee are mounted at the offset rear of the plate, while the socket is mounted to a socket mounting block attached to the fore of the plate. Flexion plates which are external to the socket, however, add undue weight, bulk, instability, and cosmetic issues.
It would be more advantageous to provide a prosthetic socket mounting block that directly facilitates mounting of the prosthetic socket to the pylon and knee, simultaneously instilling the proper flexion angle and offset in order to construct and align the diagnostic prosthesis, while the offset and angle remains within the structure of the socket device.